Various types of tripods exist for supporting cameras or other equipment during use. Single stage tripods include legs which have two portions which telescope relative to one another to adjust the total length of the leg, while dual stage tripods include legs having three telescoping portions. Although single stage tripods are more versatile than non-adjustable tripods, dual stage tripods provide an added level of control and adjustability over single stage tripods.
The separate, telescoping portions of a leg are coupled together by a lock assembly to prevent relative movement when the supported equipment is in a desired position. The lock assembly is generally secured to the end of one leg portion and slidingly engages the second leg portion. For example, the lock assembly of a single stage tripod leg is typically secured to the lower end of the upper leg portion, and slidingly receives the lower leg portion. When the telescoping leg portions reach their desired position, the lock assembly is engaged to couple the upper and lower leg portions together to prevent any further movement.
While various types of lock assemblies exist for securing the leg portions together, they typically include elements that either clamp the leg portions together using a substantially horizontally exerted force, physically engage an opening in one of the leg portions, or both. The lock assembly may be actuated by a knob or a lever disposed substantially adjacent the lock assembly itself. Alternately, in single stage tripods, the legs may be remotely actuated. This allows the user to readily adjust the leg locks while stabilizing the tripod head. For example, in U.S. Pat. No. 4,840,338 to O'Connor, the lock assembly secured to the lower end of the upper leg portion of a single stage tripod is actuated by means of a cable which runs from the lock assembly to the head of the tripod. An upward actuating force is exerted on the cable by means of either a rotating ring or collar, or an actuating lever which force is further transmitted onward to the lock assembly. This remote actuation is possible because the relative distance between the upper end of the tripod leg and the lock mechanism secured to the lower end of the upper portion of the leg remains constant even during-telescoping movement.
With a dual stage tripod, however, the distance between the lower lock assembly (which couples the middle and lower leg portions) and the upper end of the tripod leg does not remain substantially constant. Rather, as the upper and middle leg portions telescope, the distance between the lower lock assembly and the upper end of the leg necessarily changes. Accordingly, prior art methods of remote activation may not be used with the lower locks of a dual stage tripod. As a result, dual stage tripods are not so readily utilized or quickly set up because the user must stabilize the tripod head in a desired position while reaching down to secure each of the locks of each of the legs.